This invention relates to electric machines and systems related thereto, and more particularly to cooling one or more components of the electrical machines.
In an electrical machine, such as a motor and/or generator, the stator and the rotor are subject to resistive loss heating, inductive heating from eddy currents, hysteresis, and aerodynamic heating caused by the friction of air or gas present in the gap between the rotor and the stator. The bearings are also subject to friction heating. In certain applications, the rotor, stator, and bearings may be subjected to heating from thermal conduction or “soak back” from the actuator or prime mover that is connected to the machine.
It is desirable to maintain temperatures within the electrical machine within specified ranges to prevent deleterious effects caused by excessive temperatures, such as, for example, insulation breakdown, excessive expansion leading to rubbing or imbalance, yield failure or creep, cyclic fatigue, bearing failure, and damage to or demagnetization of permanent magnet materials. Moreover, high speed electrical machines, i.e., electrical machines operating at speeds above 3,600 revolutions per minute (“RPM”) compared to conventional electrical machines operating at speeds between 1,800 and 3,600 RPM, have power densities, by both volume and weight, much higher than conventional electrical machines. As a result, heat generated by high speed electrical machines is more concentrated in a smaller volume or surface compared to conventional electrical machines.
Methods using fans and air or other gas or liquid coolants provided from an external source have been used to provide cooling to electrical machines. However, in the context of high speed electrical machines, such cooling methods do not provide a reasonable technical and cost effective cooling solution. Particularly, in order to cool high speed electrical machines, a large pressure head is generally necessary due to small volume and small gaps between the rotor and the stator. Fans presently utilized to cool electrical machines become a heat source when operated at high speeds and, therefore, exacerbate the cooling problem associated with high speed electrical machines, especially when it is required to generate large pressure head.
Utilizing multiple fans in a back-to-back configuration are not a cost effective solution for industrial electrical machines. External sources for providing gas or liquid coolants to cool high speed electrical machines also add cost and complexity. Consequently, there is a need in the art to cool various components of electrical machines, such as, for example, stators, rotors, and bearings, in a simple and relatively inexpensive manner so that the electrical machines will remain within a specified temperature range.